This disclosure relates to imaging members and, more specifically, to imaging members having a surface layer possessing excellent charge transport properties and in embodiments resistance to wear.
In the art of electrophotography, an electrophotographic member comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The member is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example, from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member, such as paper.
The imaging members, that is, photoreceptors, can take several forms, including flexible belts, rigid drums, plates, and the like. Electrophotographic photoreceptors can be prepared with either a single layer configuration or a multilayer configuration. Multilayered photoreceptors may generally include a substrate support, an electrically conductive layer, an optional charge blocking or hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional protective or overcoating layer(s). In the multilayer configuration, the active layers of the photoreceptor are the charge generation layer (CGL) and the charge transport layer (CTL). For multilayered flexible photoreceptor belts, an anticurl layer can be selected for the backside of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoreceptor flatness.
It may be desirable to enhance charge transport in photoresponsive surface layers of photoreceptors to alter their performance characteristics. In some situations, charge transport can be achieved with high-mobility charge transport molecules, specifically also known as hole transport molecules (HTM), and/or high HTM loading in a surface layer of a photoreceptor, such as a charge transport later. Another approach to enhance transport is incorporation of a relatively non-polar polymeric component in a polymeric matrix forming a surface layer of a photoreceptor: for example, N,N′-diphenyl-N,N-bis(3-methyl phenyl)-1,1′-biphenyl-4,4′-diamine in polystyrene exhibits higher mobility than the same aryl amine molecule in polycarbonate. Drawbacks to the above approaches include difficulties with synthesis, crystallization of the HTM at high loading, and poor mechanical properties after prolonged use of the resulting surface.
In addition, wear resistance of the top surface layer may be desirable for long life photoreceptors. In some instances, wear resistance of a surface layer may be moderately improved by doping with low surface energy polytetrafluoroethylene (PTFE) micro-particles, or nanosized metal oxides such as Al2O3. However, because preparation of a dispersion to achieve such doping is difficult, homogeneous systems are sometimes selected due to their simplicity in manufacturing.
Improved methods for forming photoreceptors, including charge transport layers, remain desirable.